• Analysis of symptom diaries kept by 256 pregnant women shows that is inaccurate to describe nausea and vomiting in pregnancy as 'morning sickness'

• Team led by University of Warwick finds that symptoms can occur at any time of the day

• Although likelihood of experiencing symptoms is highest in the morning, nausea was still likely to occur later in the day

• First time that the symptom patterns of nausea and vomiting in pregnancy have been mapped

The term 'morning sickness' is misleading and should instead be described as nausea and sickness in pregnancy, argue researchers led by the University of Warwick who have demonstrated that these symptoms can occur at any time of the day - not just the morning.

The researchers call for the change in a study published today (30 June) in the British Journal of General Practice which shows that, while the most likely time for pregnancy sickness symptoms to occur is in the morning, a significant number of women can experience them at any time of the day.

'Morning sickness' has long been used to describe nausea and vomiting that women often experience in the early stages of pregnancy. Although pregnant women often report experiencing nausea and sickness throughout the waking day, until now no research has described the likelihood of these symptoms occurring at different times of the day. 

For this study, the researchers used data from daily symptom diaries kept by 256 pregnant women. In these diaries, the women recorded their experience of nausea and vomiting for each hour in the day, from the day they discovered they were pregnant until the 60th day of their pregnancy. The researchers then used this data to map the likelihood of experiencing nausea and experiencing vomiting in each hour of the day, broken down into weeks following last ovulation.

They found that whilst vomiting was most common between the hours of 7.00 am and 1.00 pm, nausea is highly likely throughout the whole daytime, not just the morning. Furthermore, many women still reported vomiting as a symptom even into the evening. The most common hour for participants to experience nausea and vomiting was between 9.00 am and 10.00 am with 82% experiencing nausea in this hour, and 29% experiencing vomiting. 

94.2% of participants experienced at least one of these symptoms during the study, with 58% experiencing both.

In addition, by comparing occurrence of symptoms across the first 7 weeks of pregnancy, measured from last ovulation, the researchers found that the later the week, the higher the probability of experiencing symptoms. The probability of experiencing nausea is at its highest in weeks 5, 6 and 7 while for vomiting it is in week 7. As the study only examined the first seven weeks of pregnancy, the probabilities after week 7 are not known.

Professor Roger Gadsby, of Warwick Medical School, said: "Morning sickness is widely used by the general public, media and even healthcare professionals but it doesn't give an accurate description of the condition.

"If a pregnant woman experiences sickness in the afternoon she may feel that this is unusual and wrong, or if she experiences no vomiting but feels nauseated all day she might think she is not covered by the term 'morning sickness'. And those women who experience severe symptoms feel it trivialises the condition.

"Nausea and vomiting in pregnancy (NVP) can have a significant negative impact on the lives of sufferers. It can cause, feelings of depression, of being unable to look after the family, and of loss of time from paid work. Very severe NVP called hyperemesis gravidarm (HG) is the commonest cause of admission to hospital in the first trimester of pregnancy."

It is estimated that the annual costs of managing nausea and vomiting in pregnancy to the NHS in England and Wales are around £62 million. 

The study authors said: "The continued use of the term 'morning sickness' could imply that symptoms only rarely occur in the afternoon and evening so that sufferers will have significant parts of the day symptom-free. 

"This study shows that this is an incorrect assumption and that symptoms, particularly nausea, can occur at any time of the day."